Bias
The diagonal direction of a woven fabric, at 45 degrees to the threads, where it stretches the most.
Cutting on the bias makes a woven fabric drape softly and gives it some stretch, which is used for skirts and dresses with a fluid fall and for bias binding that follows curves without puckering. Garments cut on the bias use more fabric, are harder to cut accurately and can drop as they hang, so they are usually left hanging for a while before the hem is marked.
Example
Bias binding is cut as strips at 45 degrees so that it can follow the curve of a neckline or an armhole without puckering.